An axial flow rotary machine, such as a gas turbine engine for an aircraft, is one example of a machine having a flowpath for hot gases which is bounded by seal structure. Such an engine typically includes a compression section, a combustion section and a turbine section. An annular flowpath for working medium gases extends axially through the sections of the engine. A stator assembly extends axially through the engine and circumferentially about the flowpath to bound the flowpath for working medium gases.
A rotor assembly extends axially through the engine. The rotor assembly has arrays of rotor blades in the turbine section. Each rotor blade extends outwardly across the working medium flowpath to receive work from the working medium gases and to drive the rotor assembly about its axis. In the compression section, the rotor assembly has compressor blades which extend radially outwardly across the medium flowpath. These blades are used to compress the incoming working medium gases.
The stator assembly includes arrays of seal assemblies disposed about the rotor assembly in the compression section and in the turbine section. Such seal assemblies might face radially outwardly or radially inwardly toward the working medium flow path. The seal assemblies block the leakage of working medium gases between the rotor assembly and the stator assembly, such as past the tips of the rotor blades, to preserve the efficiency of the engine.
Several factors affect the design of a seal assembly for the turbine section.
The seal assembly must tolerate the high temperatures of the turbine section and destructive interference with the tips of the turbine blades. Such interference may occur when inertia loads from aircraft maneuvers act on the rotor assembly. In addition, the method of making the seal assembly should avoid a high scrap rate and rework for the seal assemblies.
One typical seal assembly 40 used in the turbine section has a substrate 42 and a honeycomb-like metal structure 47 having an innermost surface 55 adjacent the array of rotor blades 28. The honeycomb-like metal structure is attached to the relatively rigid substrate. The substrate is typically formed of sheet metal or a forged ring which is disposed about the rotor blades and is segmented to accommodate thermal expansion and contraction of the stator assembly. The substrate in turn is supported from adjacent structure of the stator assembly to position the substrate and honeycomb-like metal structure radially with respect to the array of rotor blades.
An example of such a metal structure 47 is shown in FIG. 3 and is labeled prior art. The substrate 42 has an upstream end 49 and a downstream end 50 which adapt the substrate to engage the adjacent stator structure of the engine. The substrate has a reference axis A.sub.s. A first surface 44 extends axially with respect to the axis A.sub.s and is a frustoconical arcuate segment in shape. A second surface 46 extends at an obtuse angle alpha to the first surface in a direction which is substantially parallel to the axis A.sub.s. The second surface is a cylindrical segment in shape.
Two separate strips of honeycomb-like material are bonded to the substrate: one piece of honeycomb 47a is bonded to the frustoconical surface; the other piece of honeycomb 47b is bonded to the cylindrical surface.
Very few problems were encountered in attaching the cylindrically shaped portion of the honeycomb to the cylindrically shaped surface of the substrate. Many problems were encountered in attaching the frustoconically shaped piece of honeycomb to the frustoconically shaped surface of the seal assembly. In particular, delamination of the honeycomb material from the substrate would occur as shown in FIG. 3 at the region of the honeycomb that had the greatest radial height from the axis A.sub.s. This delamination appeared in the finished article which was first welded and then bonded.
Fabrication of the part typically involved two steps. The first step was to weld the honeycomb to the substrate, such as by resistance welding although TIG tack welding might be employed. This required urging the honeycomb structure against the substrate to ensure that good contact occurred between the honeycomb structure and the substrate. Typically, special fixturing was employed to locate the honeycomb with respect to the substrate in the axial direction. After bonding, delamination of the honeycomb structure from the substrate was often found to have occurred on the frustoconically shaped surface.
Accordingly, scientists and engineers working under the direction of Applicants' Assignee have sought to solve the problem of delamination and to develop a method for bonding honeycomb to the frustoconically shaped surface that would reduce the rate at which delamination occurs during the manufacturing process and to reduce the need for special fixturing of the honeycomb.